The present invention relates to an improvement of an electronic watch, in particular to an electronic watch for reduction of current consumption of an integrated circuit (hereinafter referred to as "IC") and for reduction in size of the IC.
In general, a reference voltage of a comparator circuit (hereinafter referred to as "comparator") has been used as a given value using a constant voltage without depending on a supply voltage. However, when a constant voltage circuit exclusive to the reference voltage of a rotation detecting comparator is employed in an IC for an electronic wristwatch, a circuit structure becomes increased in size, and in the case where a volume is restricted as in the electronic wristwatch, an IC area is reduced as much as possible, as a result of which the constant voltage circuit is unsuitable for the IC of the electronic wristwatch. For that reason, the reference voltage of the rotation detector circuit in the electronic wristwatch as conventionally used is the supply voltage or a voltage obtained by dividing the supply voltage by resistance.
FIG. 2 shows an example of the periphery of a rotation detector circuit using a voltage obtained by dividing the supply voltage by resistance as the reference voltage of the rotation detector circuit in a conventional electronic watch.
The respective gates of a detection element Pch-Tr 201, a detection element Pch-Tr 202, a motor driver Pch-Tr 205, a motor driver Pch-Tr 206, a motor driver Nch-Tr 207 and a motor driver Nch-Tr 208 are connected to a pulse synthesizing circuit not shown which synthesizes signals divided according to a reference signal from an oscillator circuit to produce a drive pulse, a correction pulse, a rotation detection pulse and so on. A voltage (minus side input terminal) of a rotation detecting comparator 210 at a detected side thereof is a terminal voltage (hereinafter referred to as "VRS") of a resistant element 203 or 204 which is developed when applying the rotation detection pulse thereto. On the other hand, a reference (plus side input terminal) is a voltage obtained by dividing the supply voltage by a reference voltage resistor 211 and a reference voltage resistor 212. The rotation or non-rotation is detected according to whether the VRS is larger than the reference voltage or not. Also, the VRS during rotation (hereinafter referred to as "rotation VRS") is in proportional to the fluctuation of the supply voltage whereas the VRS during non-rotation (hereinafter referred to as "non-rotation VRS") has a characteristic such that it is a given value without almost depending on the fluctuation of the supply voltage.
In the case where the reference voltage is a supply voltage or a voltage obtained by dividing the supply voltage by resistance, the reference voltage of the rotation detecting comparator is also caused to fluctuate according to the fluctuation of the supply voltage. For that reason, a stepping motor is designed taking the fluctuation of the reference voltage into account. Then, in the case where the reference voltage is the supply voltage, there is the possibility of detecting an actually rotating state as non-rotation in error because there is not a large difference between the reference voltage and the rotation VRS. In order to prevent such misdetection, the stepping motor is designed such that the rotation VRS is highly outputted. However, even if the design constant of the stepping motor is changed, a value of the rotation VRS is not largely changed. Therefore, in the case where the reference voltage is a voltage obtained by dividing the supply voltage by resistance, the reference voltage can be set to an arbitrary voltage, which is most useful. However, because resistors are required, and also high resistance is required to suppress current consumption, an area of the IC is increased.